LHRH neurons, critical for reproduction, are derived from the nasal placode and migrate into the brain where they become integral members of the hypothalamic-pituitary-gonadal axis. We study mechanism(s) underlying LHRH neuronal differentiation, migration and axonal targeting in normal/transgenic animals, and nasal explants. Intrinsic and trans-synaptic regulation of LHRH gene expression, peptide synthesis and secretion in LHRH neurons are studied using nasal explants, cell lines and normal and transgenic animals. Previous work in our lab 1) showed that outgrowth of olfactory axons and migration of LHRH neurons occur in isolated olfactory pit tissue, 2) revealed olfactory axon 'guidance cues' localized to midline nasal cartilagenous tissue, 3) showed GABA was an important factor in the migration of LHRH neurons in nasal regions and 4) identified a novel gene termed NELF. We hypothesize NELF acts via a homophilic interaction to influence LHRH neuronal migration on olfactory axons. Over the past year, we have continued our work characterizing the expression pattern of NELF during development. NELF is primarily limited to PNS and CNS tissues, being highly expressed in the thalamus both prenatally and postnatally. We have worked throughout the year to generate a NELF knockout and currently have chimeric animals that are being bred. Future studies are directed at understanding the role of NELF during development and the downstream signals activated by this molecule that result in axon outgrowth and cell movement. To understand the regulation of LHRH neurons and their cellular responses, we examined the activity of LHRH neurons in nasal explants. We found that there are important maturational events that are intrinsic properties of these cells such as biosynthesis of peptide product. We have also demonstrated that LHRH neurons maintained in vitro can release LHRH peptide and rapidly synthesize new peptide in response to a secretory event. Work in progress is focused on: 1) isolation of the midline cues which influence olfactory axon outgrowth; 2) the role of NELF and other molecules in LHRH migration, 3) whether LHRH neurons maintained in nasal explants (devoid of brain influences) show rhythmic activity patterns and if so the mechanisms underlying this rhythm, and 4) genes differentially expressed in LHRH neurons as a function of GABAergic stimulation.